The histone deacetylase (HDAC) family of transcriptional co-repressors, currently comprising 18 members, are emerging as important regulators of colon cell maturation and transformation. For example, inhibitors of HDAC activity including the short-chain fatty acid butyrate, induce classical cell maturation effects on colon cancer cells in vitro, while overexpression of HDACs 1 and 2, inhibits intestinal cell differentiation. Consistent with these findings, we have now demonstrated that the class I HDAC, HDAC3, promotes cell proliferation and survival of colon cancer cells in vitro, and that it represses expression of p21, and the marker of colon cell differentiation, alkaline phosphatase. We have also demonstrated that HDAC3 expression is upregulated in human colon cancer and that it is maximally expressed in the proliferative compartment in normal mouse small intestine and colon, collectively implicating a role for this specific HDAC in maintaining intestinal cell proliferation and inhibition of cell maturation. Importantly, the expression pattern of HDAC3 parallels that of (B-catenin-TCF-MYC signaling, a major regulator of intestinal cell maturation, and the fundamental signaling pathway deregulated in colorectal tumorigenesis. Our primary hypothesis, therefore, is that (B-catenin-TCF-MYC signaling activates HDAC3 expression, which in turn, plays a role in maintaining cell proliferation and inhibiting differentiation of colonic and small intestinal epithelial cells. To directly test this, we will: 1. Determine whether HDAC3 expression is regulated by B-catenin-TCF-MYC signaling in intestinal cells. 2. Determine the effect of intestine-specific HDAC3 overexpression on cell maturation programs and tumor formation in vivo. We have generated a transgenic mouse (Villin-HDAC3- Tg), in order to overexpress HDAC3 in an intestinal-specific manner, and along the entire length of the crypt and crypt-villus axes. 3. Dissect the molecular mechanism by which HDAC3 mediates its phenotypic and transcriptional effects in colon cancer cells. Specifically, the role of the co-repressor proteins NCoR and SMRT and that of other class I and II HDACs in mediating the HDAC3 response will be addressed using an integrative gene expression profiling and ChIP on chip strategy. These studies are designed to provide insights into the role of HDAC3 in regulating intestinal cell maturation in vivo, and to define these effects in the context of existing paradigms of intestinal cell maturation and transformation. Additionally, given the current interest, and recently demonstrated efficacy of HDAC inhibitors in cancer treatment, these studies are designed to provide insights into the likelihood that this class of compounds will be efficacious in the treatment of colon cancer.